We investigate the nonequilibrium electronic structure of 1T-TaS2 by time- and angle-resolved photoemission spectroscopy. We observe that strong photoexcitation induces the collapse of the Mott gap, leading to the photo-induced metallic phase. It is also found that the oscillation of photoemission intensity occurs as a result of the excitations of coherent phonons corresponding to the amplitude mode of the charge density wave (CDW). To study the dynamical change in the band dispersions modulated by the CDW amplitude mode, we perform analyses by using frequency-domain angle-resolved photoemission spectroscopy (FDARPES). We find that two different peak structures exhibit anti-phase oscillation with respect to each other by retrieving the amplitude and phase parts of the FDARPES spectra. They are attributed to the minimum and maximum band positions in energy, where the single band is oscillating between them synchronizing with the CDW amplitude mode. We further find that the flatband constructed as a result of CDW band folding survives during the oscillation while the Mott gap is significantly reduced. Our results suggest the CDW phase is robust, and the lattice modulation corresponding to the CDW amplitude mode dynamically modulates the Mott gap.

中文翻译：

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莫特绝缘电荷密度波态下光激发 1T-TaS2 光电子能谱的相位分辨频域分析

我们通过时间和角度分辨光电子能谱研究了 1T-TaS2 的非平衡电子结构。我们观察到强光激发引起莫特间隙的坍塌，导致光致金属相。还发现，光发射强度的振荡是由于对应于电荷密度波 (CDW) 的振幅模式的相干声子的激发而发生的。为了研究由 CDW 振幅模式调制的带色散的动态变化，我们使用频域角分辨光电子能谱 (FDARPES) 进行分析。通过检索 FDARPES 光谱的振幅和相位部分，我们发现两个不同的峰结构相对于彼此表现出反相振荡。它们归因于能量中的最小和最大频带位置，其中单个频带在它们之间振荡，与 CDW 振幅模式同步。我们进一步发现，由于 CDW 带折叠而构造的平带在振荡期间仍然存在，而莫特间隙显着减小。我们的结果表明 CDW 相位是稳健的，并且对应于 CDW 振幅模式的晶格调制动态调制莫特间隙。